In a number of industrial fields it is necessary to wind a web material around a winding spindle or core that is subsequently extracted from the completed log. Particularly in the field of paper converting, for instance, in the production of logs of toilet paper, kitchen paper or other so-called “tissue” paper products, rewinding machines are used that wind a preset quantity of web material around a central winding core. In some cases, this central winding core consists of a tubular element made of cardboard or plastic that remains inside the log. In other cases, the winding spindle or winding core is extracted from the completed log so that the log can be further processed, e.g. divided into rolls of smaller axial dimension, and packaged without the winding core or spindle inside. The winding spindles extracted from the logs are recycled and returned to the rewinder.
U.S. Pat. No. 6,565,033 describes a rewinder that uses a system for winding on a removable spindle. In this case, the removable spindle is made in two coaxial portions that are coupled together to form a complete spindle, on which the log is wound. Once the log has been completed, it is unloaded from the rewinder and the spindle is extracted, removing the two spindle portions from the two opposite ends of the finished log. This solution offers a number of advantages, particularly enabling a better distribution of the space needed alongside the rewinder to complete the spindle extraction process, as well as halving the time it takes to remove the spindle from the log, given the same extraction rate. In addition, extracting the two spindle portions from opposite sides of the log enables the friction forces between the semi-spindles and the wound material to be balanced, thereby reducing or eliminating the force that would otherwise have to be exerted to keep the log axially steady while the spindle is removed.
The steps needed to extract the spindle are completed while the spindle is retained at an extraction station downstream from the log winding area. These spindle extraction steps take a certain amount of time and occupy a part of the processing line. Extractable spindles are currently used for winding logs of relatively large dimensions, i.e. containing relatively large quantities of web material, that consequently take a considerable amount of time to wind (typically several seconds). In this case, the time taken to complete the winding process is compatible with the time it takes to extract the spindles from the log being unloaded from the rewinder.
There are also rolls of paper or other web material on the market, however, on which only a limited quantity of material is wound and they consequently take very little time to be wound (typically 1-2 seconds). In addition, the growing tendency to produce faster and faster rewinders leads to a continuous reduction in the time taken to wind a single log.
When the log winding time becomes so short (either because of the high speed of the rewinder or because of the limited amount of material wound onto each log), the use of removable spindles becomes troublesome because the extraction of the spindle becomes a step with a far from negligible influence on the total time taken to produce a log.
EP-A-135662 describes a rewinder in which the winding process takes place around tubular cores that engage at the ends with tailstocks moving along a closed path that extends from a position for gripping the tubular winding cores to a winding area between winding belts, and from there to and unloading area. The tailstocks are movable so that they can engage with and release the single winding cores.